Riveting Testimony in Case That Triggered Nationwide Protests

A key prosecution witness offered riveting testimony Wednesday about her phone conversation with 17-year-old Trayvon Martin moments before he was fatally shot by George Zimmerman, who was charged with murder following their nighttime encounter last year in Sanford, Fla.

Mr. Zimmerman faces second-degree murder charges for allegedly pursuing and killing the unarmed teenager, in a case that triggered nationwide protests. He has pleaded...